1. Field of the Invention
The present invention relates to an image stabilizer which stabilizes image blurred by vibration or the like at the time of shooting; a lens barrel which has the image stabilizer; and an imager apparatus such as a digital still camera or video camera, incorporating the lens barrel.
2. Description of the Related Art
In recent years, performance of an imager apparatus such as a digital still camera and a video camera has been improved remarkably, and it became possible for anyone to easily shoot still pictures and moving pictures with high image quality and with high efficiency. Improved efficiency of such an imager apparatus owes to high performance of an imager apparatus such as a lens, a CCD and CMOS, and an image processing circuit.
However, even though the lens, the CCD and the like can be made higher in performance, if hand shake or vibration occurs in photographer's hands by which a camera (imager apparatus) is held, blurring occurs in images with high resolution and shot images are blurred. To solve this problem, a part of relatively expensive cameras is equipped with an image stabilizer capable of stabilizing images blurred by camera shake and the like upon image pickup. However, cameras that require such image stabilizer are not professional-level cameras, and it is to be understood that image stabilizers are indispensable to consumer cameras for a large number of amateur photographers with less shooting experience.
Further, in general, a demand for smaller and lighter cameras (imager apparatuses) is strong and most of photographers like cameras which are light in weight and easy to carry. However, since an image stabilizer in related art is comparatively large in size, when such large image stabilizer is mounted on a camera body, the whole of the camera becomes large in size, which is against a demand for making cameras smaller in size and lighter in weight. In addition, image stabilizers in related art require a large number of components and a problem arises, in which a cost of cameras increases as the number of components is increased.
As this kind of image stabilizer in related art, there is an image stabilizer described in Patent Literature 1, for example. In Patent Literature 1, there is described the one relating to a vibration-prevention device provided in a camera or the like, which detects camera shakes relatively low in frequency and uses the detected results as information for the prevention of image blurring, thereby preventing image blurring. This vibration-prevention device described in Patent Literature 1 (hereinafter referred to as “a first related-art example”) is a vibration-prevention device for a camera, including: a correcting optical mechanism, a vibration detector and a vibration-prevention controller. The correcting optical mechanism is provided inside a lens barrel holding a lens group and deviates the optical axis of the lens group. The vibration detector detects vibration applied to the lens barrel. The vibration-prevention controller prevents vibration by driving the correcting optical mechanism based upon a signal from the above-described vibration detector. The correcting optical mechanism has: a correcting lens, a fixing frame, a first holding frame, a second holding frame, first and second coils, first and second drivers, and first and second position detectors. The fixing frame fixes the correcting lens. The first holding frame holds the fixing frame in such a manner that the fixing frame can be moved in the first direction different from the optical axis direction of the lens group. The second holding frame holds the first holding frame in such a manner that the first holding frame can be moved in the second direction different from the optical axis direction and the first direction, and is fixed to the lens barrel. The first and second coils move the first and second holding frames in the first and second directions, respectively. The first and second drivers are formed of first and second magnetic field generating members facing the first and second coils. The first and second position detectors detect the amount in which the fixing frame and the first holding frame are moved in the first and second directions. And at least one of the first and second magnetic field generating members and the first and second position detectors are provided in a fixed member including the second holding frame, fixed to the lens barrel.
According to the vibration-prevention device with the structure described in Patent Literature 1, there can be expected the effectiveness in which the vibration-prevention device can respond to vibration up to high-frequency vibration without increasing the cost and the large space.
As another example of an image stabilizer in related art, there is an image stabilizer described in Patent Literature 2, for example. In Patent Literature 2, there is described the one relating to a camera image blurring restrainer in which vibration (camera shakes) of approximately 1 Hz to 12 Hz in frequency applied to an apparatus such as a camera are detected to be used as information for restraining image blurring, thereby preventing image blurring. This camera image blurring restrainer described in Patent Literature 2 (hereinafter referred to as “a second related-art example”) calculates a correction amount of deviating the optical axis necessary for restraining image blurring on an image surface, based upon detected information on vibration applied to a lens barrel. And, according to the above-mentioned correction amount, the image blurring restrainer controls movement of a correcting optical system supported in a floating manner so as to be moved in the diameter direction of the lens barrel. Regarding the support of the above-mentioned correcting optical system in a floating manner, there are provided a first holding frame and a second holding frame. The first holding frame supports the correcting optical system in such a manner that the correcting optical system can be moved in the first direction set within a plane that is perpendicular to the optical axis, but restricts movement in other directions than that. The second holding frame supports the second holding frame in such a manner that the second holding frame can be moved in a second direction that is different from the first direction within the above-mentioned plane, but restricts movements in other directions than that. And, this second holding frame is fixed to the lens barrel.
According to the camera image blurring restrainer with the structure described in Patent Literature 2, there can be expected the effectiveness in which there is no problem of being out of focus at the time of restraining image blurring. Also, since the correcting optical mechanism can be constructed with its size being small in the direction of the optical axis, there can be expected the effectiveness in which a camera can be small-sized.
Also, as yet another example of an image stabilizer in related art, there is an image stabilizer described in Patent Literature 3, for example. In Patent Literature 3, there is described the one relating to a lens drive device of an optical apparatus. This lens drive described in Patent Literature 3 (hereinafter referred to as “a third related-art example”) is a lens drive device including: a first driver and a second driver. The first driver drives a lens storage portion holding a lens in a first direction within a plane that is perpendicular to the optical axis of the above-described lens. The second driver drives the lens storage portion in a second direction perpendicular to the first direction within the plane. And, the first driver and the second driver are aligned along an axis parallel with the optical axis of the lens.
According to the lens drive device with the structure described in Patent Literature 3, there can be expected the effectiveness in which a lens drive device that drives a correcting lens for stabilizing blurred images can be small-sized.
[Patent Literature 1] Japanese Published Patent Application No. H3-186823
[Patent Literature 2] Japanese Published Patent Application No. H3-188430
[Patent Literature 3] Japanese Published Patent Application No. H10-311995
However, regarding the first and second related-art examples, the area as regards an image stabilizer becomes large in the directions perpendicular to the optical axis of a correcting lens, so that there is not only a problem in which a lens device and an imager apparatus are made large as a whole, but also a problem that the number of components increases, which results in considerable cost increase. Specifically, regarding the first and second related-art examples, a fixing frame having a correcting lens is roughly formed into a square shape, a pair of yaw shafts are disposed outside the fixing frame on both sides in the lengthwise direction, and a pair of pitch shafts are disposed outside the fixing frame on both sides in the widthwise direction. Further, pitch coils are attached to both ends of the fixing frame in the lengthwise direction, and each pitch coil is provided inside a first magnetic circuit made of a magnet and a yoke.
Regarding the pair of pitch shafts, both ends thereof are supported by a first holding frame, and the fixing frame is supported in such a manner that the fixing frame can move in a pitch direction with respect to this pair of pitch shafts. Also, regarding the pair of yaw shafts, both ends thereof are supported by the first holding frame, and a pair of housings fixed to a second holding frame are fitted on this pair of yaw shafts in a freely slidable manner. Further, a pair of yaw coils are attached to the outside of the pair of yaw shafts of the first holding frame, and each yaw coil is provided inside a second magnetic circuit made of a magnet and a yoke.
Thus, by applying electric current to the pitch coils of the first magnetic circuit, the fixing frame having the correcting lens is driven in a pitch direction regarding the first holding frame. Also, by applying electric current to the yaw coils of the second magnetic circuit, the fixing frame having the correcting lens is driven in a yaw direction regarding the second holding frame, integrally with the first holding frame.
However, in the case of the first and second related-art examples, a structure is employed in which a magnet and a yoke are necessary for both an actuator for driving a correcting lens in a first direction (for example, a pitch direction) and an actuator for driving the correcting lens in a second direction (for example, a yaw direction), and those actuators are disposed in such a manner as to surround all sides of the correcting lens. For that reason, an image stabilizer becomes large in the directions perpendicular to the optical axis of the correcting lens, hence the above-mentioned problem in which the whole of device is enlarged and the number of components increases, occurs, thereby leading to cost increase.
Also, in the third related-art example, coils of a first actuator for driving a correcting lens in a first direction and of a second actuator for driving the correcting lens in a second direction are both constructed of flat coils which are wound to expand in a direction parallel with the optical axis of the correcting lens. For that reason, a magnet and a yoke for the first actuator and a magnet and a yoke for the second actuator are separately required, hence a large number of components are required to make the number of processing and assembly processes increase, which leads to a problem of cost increase.
Further, between the yoke for the first actuator and the yoke for the second actuator is provided one center yoke which serves as a yoke for the two actuators. As a result, the magnetic flux density of each of the magnets of the first and second actuators has to be prepared by one yoke, so that it is necessary to provide in a predetermined position a center yoke which is twice as thick and capable of saturating the magnetic flux density of each magnet. For that reason, the area of an image stabilizer becomes large in the directions perpendicular to the optical axis of the correcting lens, thus causing a lens barrel and an imager apparatus as a whole to be large.
Also, in the first, second and third related-art examples, a holding frame which has a correcting lens is guided and supported in a movable manner in a first direction and a second direction perpendicular to each other; and the guide supporting mechanism is formed of a combination of a shaft and a bearing portion, each forming a pair with two sets thereof. In this case, there may be required a gap of a certain size between the shafts and bearings to allow the holding frame to move, thereby causing rattle at the time of the movement, which makes smooth movement difficult and makes the position of the correcting lens unstable.